1. Field of the Invention
This invention relates to an interchangeable lens assembly of a camera, and more particularly to a lens unit which may be attached to and detached from a camera body with ease while preserving accurate and reliable angular alignment of the diaphragm mechanism of the unit to that part of an automatic exposure control apparatus which is incorporated in the camera body.
2. Description of the Prior Art
Interchangeable lenses such as standard, wide angle, telephoto or zoom lenses, may be coupled to a camera body by several methods, and the conventional types of coupling devices may be classified into three main categories. One such device is called a "multi-revolution screw coupling". This device is constructed with a male screw thread formed on a rear end outer diameter of a main support tube in which the objective is mounted and a female screw thread formed on the inner diameter of a bore provided through the wall of the front panel of the camera housing. When the interchangeable lens is joined to the camera body, the tube is turned in adaptation to the bore until the radial shoulder of the tube abuts against the front panel. As the tube is driven to advance by the action of the helix angle, it is tightened by the frictional force exerted between the bearing surfaces as a result of the wedge effect created thereon. Such coupling requires the establishment of accurate correspondence between the male and female threads, and it is therefore troublesome and often cannot be rapidly established. Further, because of the necessity that the tube be turned through a large number of revolutions, the coupling is time-consuming. An additional serious disadvantage is that the final angular position of the tube relative to the camera body varies depending upon the torque applied to the tube.
The second category is called "bayonet coupling". This device comprises male and female bayonet members provided respectively on the tube and the camera housing. During the coupling operation, the male bayonet member is slidably inserted into the female bayonet member and then turned by rotating the tube about the optical axis of the lens, while the camera housing is maintained stationary. An advantage of this coupling device is that the final angular position of the tube relative to the camera housing can be determined with high accuracy by an abutment pin provided on the tube or on the camera housing for mechanically or electrically introducing a manually preset value of diaphragm aperture from the tube into the camera body and for automatically closing down the diaphragm as controlled from the camera body.
When the tube is tightened on the camera housing, however, rotation of the tube is required which in turn causes movement of transmission members which project from the tube into a space within the camera housing. Accordingly, the camera housing specified for use with such tube must be designed so that nothing is located in the paths of movement of the transmission members. Thus, such camera housing can not be interchanged with other types of camera housings, and this characteristic of the coupling device prejudices the usefulness of and interchangeability thereof. Another disadvantage arising from a plurality of transmission members is that, as it is impossible to clear up the space through which the transmission members are moved during the coupling operation, the control members for the transmission members in the camera housing must be provided with buffering means to avoid mechanical interference which would be otherwise encountered between the transmission members and the control members in sequence.
The third category coupling device which has overcome the drawbacks of the second category is typically disclosed in U.S. Pat. No. 3,906,534, in which one of the two bayonet coupling members corresponding and complementary with each other is made moveable with reference to its carrier, that is, the tube, or the camera housing, and is constructed in the form of a ring arranged to be journalled around an adapter shell which constitute the rear part of the tube. After the adapter shell of the tube is slidably fitted into the bore of the camera housing, the aforesaid moveable ring is brought into angular alignment with the corresponding and complementary coupling member, and then turned in a tightening direction, while the adapter shell remains stationary.
This type of coupling device assists in achieving accurate and reliable establishment of operative connection between the diaphragm responsive transmission and the control device therefor in the camera body regardless of the number of transmission components provided. Also, the common disadvantage of the aforesaid first and second categories can be eliminated. For example, the occurrence of deviation of the axial position and flatness of the abutment surfaces of the adapter shell and the camera housing caused by the wearing-out of the abutment surfaces due to the frictional relative movement of one abutment surface to the other can be eliminated. But, an alternate disadvantage is introduced because of the requirement of locating the coupling ring at a point within a longitudinally small space in the vicinity of the abutment surface of the adapter shell. Thus, the accessibility to and the management of the coupling ring are not sufficiently secured. Particularly with cameras emphasizing convenience, the diaphragm ring, focusing ring and other actuating members are arranged on a common support tube which is short in the longitudinal direction. Thus, the space available to receive the coupling ring of such structure is not large enough to permit the necessary input torque to be exerted by the fingers of the operator.
Attempts have been made to obviate all the above mentioned drawbacks of the conventional coupling methods by imparting relative motion to the main support tube and the adapter shell so that the operator is able to drive the coupling ring for rotation by grasping the tube while the adapter shell remains stationary. As the diaphragm mechanism is mounted in the main support tube, however, provision must be made for assuring retention of the diaphragm responsive or transmission members in accurately and reliably adjusted positions before and after the tube is attached to and detached from the camera housing. Otherwise it is impossible to achieve establishment of operative connection between the diaphragm responsive transmission and the control device therefor, as the latter assumes a predetermined position which is located either in coincidence with or slightly beyond the terminal end of returning movement of the transmission.
Accordingly, it is an object of the present invention to provide a detachable mechanical unit for mounting the objective and diaphragm of a camera, said unit being easily manageable to exert an input torque on the coupling device, while achieving accurate and reliable establishment of operative connection between the diaphragm responsive transmission and the control device therefor which is mounted in the camera body.
Another object of the invention is to provide such a device which automatically drives the diaphragm transmission to be reset in the initial position when the unit is detached from the camera housing with the diaphragm ring on the lens barrel being left in any position, regardless of whether the entire range of movement of the transmission is larger or smaller than that of rotative tightening releasing movement of the main support tube in which the diaphragm is mounted.